Twenty-three states and the District of Columbia have legalized medical marijuana, but scientific research into its appropriate uses has lagged. Dr. Mark Ware would like to change that.

Dr. Ware, 50, is the director of the Canadian Consortium for the Investigation of Cannabinoids and the director of clinical research of the Alan Edwards Pain Management Unit of McGill University Health Center. Medical marijuana has been legal in Canada for 16 years, and Dr. Ware, a practicing physician, studies how his patients take the drug and under what conditions it is effective.

We spoke for two hours at the recent meeting of the American Association for the Advancement of Science and later by telephone. Our interviews have been condensed and edited for space.

Q. How did you become interested in the medical possibilities of cannabis?

A. In the late 1990s, I was working in Kingston, Jamaica, at a clinic treating people with sickle cell anemia. My British father and Guyanese mother had raised me in Jamaica, and I’d attended medical school there.

One day, an elderly Rastafarian came for his annual checkup. I asked him, “What are your choices of medicines?” He leaned over the table and said, “You must study the herb.”

That night, I went back to my office and looked up “cannabis and pain.” What I found were countless anecdotes from patients who’d obtained marijuana either legally or not and who claimed good effect with a variety of pain-related conditions.

There were also the eye-opening studies showing that the nervous system had specific receptors for cannabinoids and that these receptors were located in areas related to pain. Everything ended with, “More studies are needed.”

So I thought, “This is what I should be doing; let’s go!”

Was getting started that easy?

Actually, not.

That summer, I went to England and considered working with a British pharmaceutical concern researching cannabinoids. But just then, a Canadian court took up the case of an epileptic who’d been arrested when he used cannabis for his seizures. The court essentially legalized medical marijuana throughout Canada.

When I heard that, it seemed like Canada was the place I should be going to. I packed up my young family and moved to Montreal. What I proposed to McGill was a clinic where we might evaluate the claims of patients about medical marijuana.

So much of what we knew about the drug was anecdotal. Some of it was folkloric. My idea was to listen to the patients’ stories and put them to a clinical evaluation.

When you first moved to Canada in 1999, what was known about medical marijuana?

We certainly knew that cannabinoids were analgesic in animal models. There were case reports floating around of people with multiple sclerosis who’d been helped.

In California, people with H.I.V. were using it for appetite stimulation, nausea and pain. Cancer patients sometimes used it to curb nausea from chemotherapy.

Since then, there have been at least 15 good-quality trials around the world. Cannabinoids are reported to help with H.I.V.-associated neuropathy, traumatic neuropathy, multiple sclerosis, pain from diabetes. There have also been a few small studies on fibromyalgia and PTSD.

When you talk about translational medicine, a drug usually moves from “bench to clinic.” But cannabis has had this unique trajectory: The patients were using it on their own, and then you had these papers, often based on a few case studies. And sometimes, you had later trials which led to drugs — like with H.I.V. patients’ using cannabis, which led to Marinol.

Tell us about some of your own research.

One investigation we published in the Canadian Medical Association Journal in 2010 studied 23 patients who used three slightly different levels of cannabis preparations and one placebo for two months. They had one puff three times a day. We found that the 9.4 percent THC level was superior to the placebo in terms of its effect on pain.

We also found that it helped with anxiety and sleep. Interestingly, our patients appeared to actually use very small quantities of the drug to control their symptoms, a lot less than recreational users.

Later this spring, we hope to take this research further by launching what we think will be the first ever longitudinal study of medical marijuana patients. We’ll follow the long-term effects of those of our regular patients who’ve been using it for chronic conditions. We’ll look at safety over the years.

Why do you think cannabis use has been generally so under-researched?

The fundamental answer is that the illegality of the drug has stigmatized most research. In Canada, people are sometimes afraid because of the perception that they are working with illegal substances, even when that’s no longer the case.

In the United States, it’s a different matter, because on the federal level, cannabis is listed as a Schedule I drug, like heroin. That means that the medical community is quite restricted in gaining access to research materials.

At the same time, there are more than 20 states where medical marijuana, to differing degrees, is legal. However, the plants grown in Colorado may be quite different from those grown elsewhere. Moreover, the medically eligible conditions vary from state to state.

This lack of standardization has been another factor making research difficult, because when you’re talking about cannabis in one state and cannabis in another, you may not be talking about the same thing.

You’ve said that physicians call you frequently for practical advice about the drug. What do they ask?

The most common question is, “How do I make the distinction between patients who want it for medical or recreational use?” The other call I get is from a clinician who wants me to take his patient and explain whatever I can.

Actually, I wish those doctors would inform themselves better; a lot of information does exist, though we need more. I believe that by not informing themselves, physicians aren’t fully serving their patients.

In Canada, for instance, we’ve noticed that our oncologists generally don’t tell their patients about medical marijuana. It’s the nurses who’ll go, “Dear, why don’t you go outside and have a puff.”

Your own Canadian Medical Association reminds its members that they are not obligated to write marijuana prescriptions because there is “insufficient evidence on clinical risks and benefits.” What is your take on their stance?

Well, I agree with them, at least on this: We need more research.

I think the time has come for us as a global community to agree on what we want to know and then go get it. And our patients need to move away from self-experimenting with substances and derivatives we don’t know about, and move to a situation where we know what they are using and where we can better help them. This isn’t going away.

A version of this article appears in print on , on Page D2 of the New York edition with the headline: Seeking the Facts on Medical Marijuana. Order Reprints | Today’s Paper | Subscribe